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E39 (1997 - 2003) The BMW 5-Series (E39 chassis) was introduced in the United States as a 1997 model year car and lasted until the 2004 when the E60 chassis was released. The United States saw several variations including the 525i, 528i, 530i and 540i. -- View the E39 Wiki

Here are a few things to check.
1. Turn on AC system and ensure that the compressor clutch and electric fan are spinning.
2. System operating lowside pressure should be around 30-32 psi. If the pressure is low, have the system professionally drained. BMW system must be evacuated, new compressor oil added and freon added to a specific weight.
3. If the compressor constantly cuts on and off, I would check for high system pressure, a bad sensor, or bad expansion valve. The AC tech will have the manifold guages to check the high and low side pressures.
Once you have the system functioning properly, a good practice is to run the AC system 5-10 minutes per month. This allows the system to cycle the freon and lubricate the seals.

A/C system pressures depend on refrigerant, ambient temperature and relative humidity as well as the specific car.
I've never seen BMW &/or E39 values. However I've attached data for a Cadillac Catera which has a similar system, i.e. R134a, variable displacement compressor and TXV (rather than fixed displacement and fixed orifice) These values will at least get you in the ballpark.

Come to think if it, is the phrase "in the ballpark" understood &/or common in Oz? Just idle curiosity.

BTW, I'd like to trade. Temperature here this afternoon is 12 F, last night -5 F. Some hot air would be quite nice for a change.

Here are a few things to check.
1. Turn on AC system and ensure that the compressor clutch and electric fan are spinning.
2. System operating lowside pressure should be around 30-32 psi. If the pressure is low, have the system professionally drained. BMW system must be evacuated, new compressor oil added and freon added to a specific weight.
3. If the compressor constantly cuts on and off, I would check for high system pressure, a bad sensor, or bad expansion valve. The AC tech will have the manifold guages to check the high and low side pressures.
Once you have the system functioning properly, a good practice is to run the AC system 5-10 minutes per month. This allows the system to cycle the freon and lubricate the seals.

Not to hijack the thread, but I have a question.... Why must you evacuate the system simply from a low.charge ? I can understand evac if there is no charge or car has been sitting, but topping off refrigerant due to a low charge seems like a harmless solution. Is there something specific to BMW AC systems that I should know about ? Thanks !

Not to hijack the thread, but I have a question.... Why must you evacuate the system simply from a low.charge ? I can understand evac if there is no charge or car has been sitting, but topping off refrigerant due to a low charge seems like a harmless solution. Is there something specific to BMW AC systems that I should know about ? Thanks !

#alwayslearning

The ONLY way to ensure a correct charge, i.e. mass of R134a, is to empty the system and and then charge to the specified mass. Pressure readings do not indicate the mass of refrigerant in the system, except to hint at severe under or over charge. People charging by pressure are running a risk, particularly of overcharging which can cause catastrophic damage to the compressor.

Another rationale is that the standard evacuation and recharge cycle includes holding the system at a strong vacuum for some time to check for leaks, i.e. determine if the charge is low due to normal seepage loss of refrigerant over years or an accelerated loss due to a newly developed leak.

While I don't claim to be an expert, I don't see anything the E39's A/C system that is unique compared to other brands. All the components and the system operation strategy are conventional.

The ONLY way to ensure a correct charge, i.e. mass of R134a, is to empty the system and and then charge to the specified mass. Pressure readings do not indicate the mass of refrigerant in the system, except to hint at severe under or over charge. People charging by pressure are running a risk, particularly of overcharging which can cause catastrophic damage to the compressor.

Another rationale is that the standard evacuation and recharge cycle includes holding the system at a strong vacuum for some time to check for leaks, i.e. determine if the charge is low due to normal seepage loss of refrigerant over years or an accelerated loss due to a newly developed leak.

While I don't claim to be an expert, I don't see anything the E39's A/C system that is unique compared to other brands. All the components and the system operation strategy are conventional.

This is correct! If your AC no longer functions, I would recommend taking it to an AC service center to have the proper amount of refrigerant put back into the system. The post-97 e39 requires a narrow range of refrigerant, 750 grams +/- 10 gms. Unless you have the proper tools to perform this service, there is NO WAY you can measure this with a simple pressure gage (ask me how I know). Too much or too little risks damaging the compressor. A slow leak of refrigerant is not uncommon. The leak may take years to manifest itself as a problem (mine takes two years before requiring a recharge).

Basically the first thing you should do is to test your outside temperature sensor, look for the first sign on your instrument cluster and check whats the reading on your temperature if its showing -40c its telling the computer that outside is hell on heart... I had the same problem and almost had to buy a new AC set , glad it was just the sensor which costs around 20bucks on amazon